1. Field of the Invention
The field of the present invention lies within the art relating to enclosed switches, and the invention concerns gas-filled enclosed relays, particularly a plastic-encapsulated relay for mounting on printed-circuit boards.
2. Background Information
Developments in relay construction are aimed, inter alia, at increasing efficiency and, thus, either reducing the relay size or improving the electrical characteristics. A significant volume reduction for high-voltage and extra-high-voltage enclosed switch gear is known, which is realizable practically only by filling the enclosures with an electronegative gas, e.g., SF.sub.6. To further increase the dielectric strength, a pressure higher than the normal atmospheric pressure is generally used and any leakage losses are compensated for by refilling. A reduction of the lower operating temperature due to an increase in the evaporation temperature of the filler gas as a result of the increased pressure is not a major factor, because such switch gear is usually operated in rooms with a sufficiently high minimum temperature.
In all prior art installations where the enclosures are filled with an electronegative gas to increase the dielectric strength, either any leakage losses of the enclosures are compensated for, or the enclosures hermetically sealed, e.g., practically leakage-free metal-glass enclosures are employed.
In the case of a plastic-encapsulated relay, however, which is to be produced at low cost, is to have a small volume, and is to be mounted on printed-circut boards, for example, this category of enclosure is not realizable; and leakage compensation is just as unsuitable. For low-cost relays for printed-circuit boards, only a tight plastic enclosure can be provided.
Plastic-encapsulated relays for printed-circuit boards are known, including gas-filled relays, in which an inert gas is generally used to enhance contact reliability. The inert gas is introduced through specific openings which are closable after the filling operation. One example is the washable relay disclosed in DE-A-3323922 (U.S. Pat. No. 4,580,005). This does not result in a significant increase in dielectric strength, however.
On the one hand, more stringent safety requirements placed on relays necessitate a higher dielectric strength, and on the other hand, smaller relay sizes are desired because of the higher component density in printed circuits. A worthwhile goal for improving performance capability is therefore to increase the dielectric strength with unchanged dimensions or to maintain the dielectric strength despite significantly smaller dimensions.